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Electronics Fan control circuit idea, what do you think?

Discussion in 'Modding' started by g0th, 14 Apr 2005.

  1. g0th

    g0th What's a Dremel?

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  2. g0th

    g0th What's a Dremel?

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    Pin 8 on the MAX6302 should be tied to 5V, this isn't shown on the schematic, sorry.
     
  3. NoMercy

    NoMercy What's a Dremel?

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    *sits there trying to work out what it does* Going to give any hints on how it works, mainly the micro supervisor?
     
  4. g0th

    g0th What's a Dremel?

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    The micro supervisor contains an oscillator, and it basically performs the role of a basic clocked synchronous state machine, but hey, i'd rather use one fancy chip then 3 stock standard 74LS logic chips.

    This is explained better in the DS/Max appnote regarding no-microcontroller Dig. Pot. applications.

    Basically, the Digital Potentimeter moves on on falling edges (or rising, don't remember) of the pin 1 signal, and such that the resistance between the wiper and the 'low end' of the 'pot' decreases if the signal on pin 2 is low and vice versa.

    So we need that element that can generate the right synchronised signals from our pushbutton inputs.

    I don't think debouncing will be too critical in our application, so i left it out.

    Can someone that understands the circuit operation please suggest any changes, improvements or faults?
     
  5. NoMercy

    NoMercy What's a Dremel?

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    It does look pretty flawless, though I've not played much with the LM317 it looks perfectly reasonable.
     
  6. SteveyG

    SteveyG Electromodder

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    Maxim do several digital potentiometers that can handle push button inputs without the need for a separate IC. It may have been the DS1802, but I cannot remember off hand. If the button was held down, it would increase/decrease the resistance at regular intervals.
     
  7. cpemma

    cpemma Ecky thump

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    Last edited: 14 Apr 2005
  8. g0th

    g0th What's a Dremel?

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    Yeah, the inbuilt pushbutton interface of the DS1802 would be sweet, unfortunately it is a log pot.
     
  9. NoMercy

    NoMercy What's a Dremel?

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    The DS1809 seems like a possible, and increments the pot every 100ms after the button is held down for 1/2 a second, or single steps if pressed for less than 1/2 a second.
     
  10. nick01

    nick01 What's a Dremel?

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    The absolute maximum rating for the DS1804 is 7V. The recommended voltage range for the output is 0 to 5V. With a resistor and a Zener diode you may be able to shift that.

    (In the following all voltages rounded to integer)
    The LM317 itself has a dropout of 2V, so it will never make more than 10V at the output. That requires 9V at the adjustment pin. From the pot you have a range of 0 to 5V, which can be shifted to 4 to 9V with a 4V Zener. Put the Zener in series with the pot output.
     
  11. g0th

    g0th What's a Dremel?

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    I think connecting the digital pot to a 555 for PWM control might be a much nicer idea.
     
  12. NoMercy

    NoMercy What's a Dremel?

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    *nods* The 555 doesn't tend to operate in the MHz, so isn't likely to cause any problems regards layout :)
     
  13. cpemma

    cpemma Ecky thump

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    Digipots like DS1804 have appreciable wiper resistance (500R) and low max current (1mA), put the two together and you've a 0.5V loss, and an opamp in between looks even more attractive. Give it a low gain (x1.5-2) and you've a bit more flexibility with the output voltage range. Then use an LDO reg and get 4-11.9V output to your fan. ;)
    is a nice system for 10W fans, but for silent running not the way2go.
     

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